The purpose of this research program is to clearly describe the composition of the avian progesterone receptor and to define structural/functional relationships among various proteins within the receptor complex. Emphasis will be one the further identification of receptor-associated proteins, description of their sites of interaction and the influence of hormone binding in such interactions. Five associated proteins have been identified, two which are common cellular heat shock proteins. Further definition and analysis of these five proteins will utilize specific antibody probes. Antibodies will also be used to screen cDNA expression libraries for cDNA clones and sequence analysis. The surfaces or domains of specific protein-protein interactions will be studied with DNA transfection experiments. Here, a number of mutant cDNA constructs for the progesterone receptor will be utilized and the mutant receptors that are expressed will be analyzed for any change in interaction with associated proteins. Finally, cell-free systems will be developed for analysis of the disruption and re-construction of receptor complexes and for studying the effects of hormone binding on such events. These studies should provide new valuable information on receptor structure, functional domains, and interaction with other cellular proteins.